\section*{Technical Abstract} % (fold)
\label{sec:Technical Abstract}

\textbf{A Balloon-borne High Altitude Camera platform - Edward Moore (CHU)}

High Altitude Weather Balloons can loft small payloads to altitudes of up to 35km, which presents exciting opportunities for research and technology. At such altitudes a payload is above the vast majority of the atmoispheric air and moisture, offering `space-like' observing conditions. Large experimental payloads loft by balloons of over a million cubic meters have maken advantage of these conditions at significantly cheaper cost than an equivalent orbital sattelite, however such projects are still of the order of millions of dollars. Recent advances in micro eletronics and sensors, along with pioneering work by groups such as Cambridge Unioversity Spaceflight, have opened up this reagion of the stratosphere to amateur experimenters using cheap latex meteorological balloons.

This project aims to investigate the feasibility and propose a design for an actively stabilised platform to be lofted by a latex balloon to 30km altitude, to explore techniques for making observations at a very reduced cost compared to current methods. A stabilised platform at such an altitude has other applications aswell, such as anetnna pointing in a communications replay application (again replacing sattelites for short-term use). 

Specific emphasis was places upon the development of an inertial measurement unit to measure attitude. Cheap MEMs sensors with certain undesired characteristics were combined with modern signal processing techniques, to obtain a good estimate of the state.

A capable flight computer with inertial measurment unit was designed and built. The flight computer has all the necessary sensor hardware and computation ability to control the proposed balloon lofted platform.

The problem of telemetry from the balloon was investigated to maximise the performance of the data link, which is severaly limited in power by regulatory body stipulations. The Frequency-shift-key telemetry stream was put into general Linear Model form and a demodulator based on Bayesian Changepoint Detection was desgined. This produced excellent results, able to detect the frequency jumps into which the data is encoded under significantly poorer signal to noise ratios that a comparative matched filter technique used by a commercially available soundcard modem application.

A method was proposed and analysed to address the greatest challenge of active stabilisation - that of actuation about the yaw axis. The proposed solution uses a reaction wheel and a motor inline with the balloon suspension to control the amount of momentum in the reaction wheel to prevent saturation. The stability of this system is checked with the Routh Hurwitz criterion.

A gondla design is given and imporatn aspects of construction materials and techniques, low tempaerature considerations and stiction minimisation are discussed.

Test flights unde latex balloons were performed to test the capabilities of the flight computer and inertial measurement unit. This provided a 'soak' environment in which to test the large number of subsystems and software processes written made for the flight computer, and their complex interations. Other important mission subsystems such as flight path prediction were checked at the same time, to help ensure the safest possible test flight of a proposed prototype.

To conclude the project, aspects of the project management, ambition and scope were analysed, improvements were proposed such as a multiple-input-multiple-output controller for attitude stabilisation, using quaternion state representation, and further work was suggested on some of the interesting developments in the project, such as changepoint techniques for demodulation.



% section Technical Abstract (end)
